Nucleotides, the building blocks of DNA are composed of four bases—A, G, C, and T. Attached to the bases are sugars and phosphates. (Get a genetics overview.)

First, researchers made XNA building blocks to six different genetic systems by replacing the natural sugar component of DNA with one of six different polymers, synthetic chemical compounds.

The team—led by Vitor Pinheiro of the U.K.'s Medical Research Council Laboratory of Molecular Biology—then evolved enzymes, called polymerases, that can make XNA from DNA, and others that can change XNA back into DNA.

This copying and translating ability allowed for genetic sequences to be copied and passed down again and again—artificial heredity.